Abrasive thinking and fractured English

A standard with the cover title Coil Coated Metals - Test Methods - Resistance to Abrasion - could be expected to describe a test method for assessing the resistance to abrasion of coil coated metals. 1 Coming from an industry which gave 'doing what it says on the tin' to the world, no less could be expected of this standard. However, unlike most paints in tins, the standard actually does not do what it says on the cover.

The scope of the standard is drawn widely, and covers the abrasion testing of all organic coatings on metallic substrates. It therefore trespasses on ground long cultivated by related British and international standards.2 Interestingly, however, the new standard does not claim to replace the British and international standards, which exist alongside the new text. The maverick nature of the document is confirmed early in the document in the 'Normative References' Section which does not conform to the internationally agreed text.3

It would have been more useful if the scope of the new document were less widely drawn; technologists familiar with abrasion testing will extract rather more from the British and international document than they do from the European one. Confining the scope to coil coatings would be an obvious benefit; confining it further to coil coatings of defined properties on defined substrates would be even better.

It is unfortunate that much of the standard has already been published elsewhere in a more readable and instructive format. Although the new standard acknowledges the 1997 publication, where change has been made, it would probably have been better and less confusing if the relevant text of the precursor document had been merely lifted into the new one.

The principle behind the test method, as now described, falls somewhat short of encapsulating the essence of the test. Happily, the new text specifies that a Taber Abraser(r) is the required instrument, which goes a long way towards explaining what the standard means. The 'principle' of the new method is stated to be that: 'A coated test panel is placed on a rotating disc under a set of two abrasive wheels mounted in parallel and symmetrically on opposite sides of the centre rotating in the reverse direction.' There is no mention of weighing, counting, or otherwise measuring in this part of the standard. There is no underlying scientific truth called up in this section, and it has to be doubted whether this section is indeed the principle of the test - it seems merely to be an operational instruction, and a particularly garbled one at that.

The way that the test is carried out is inadequately described. No action is required, for example, if the substrate is exposed during an abrasion test, other than to stop the test. It appears not even necessary to record the number of cycles of abrasion at which the test was terminated. The method also requires a 'fresh refacing disc for every 25 revolutions'. 'Refacing' may be just a typographical error - a similar word in the 1997 document is 'resurfacing', but the requirement to replace (or 'reface') something every 25 revolutions seems excessive. In any case, at least two parts of an abraser revolve; the abrasive wheels and the specimen disc. Neither would seem to be an obvious candidate for repair/replacement at short intervals: the standard specifies that the 'abrader' revolves at between 60 and 100rpm - which would imply a new 'refacing disc' every 15 to 20 seconds.

There seems little point to this standard. The only obvious (and dubious) advantage this document1 gives is to put distance between test methods for paints and test methods for coil coatings. As coil coatings are, at least arguably, paints, the distinction in fact is probably academic.

A parallel standard4 covers a test which has no precursor. The method (for assessing the adhesion of foam to 'an organic coating on a metallic substrate under wet and dry conditions') fails in its objective. The foam used as a reference material has no defined properties, other than its use as an insulating material and its two-pack nature. The impression given by the text is that the standard aims to be a quality-control test, or a screening test, for manufacturers of sandwich bonded metallic composites, rather than a standard of international aspiration.

The default method of preparing the test piece is to pour a small quantity of the reacting foam on to the surface to be tested and leave it to set. The polymerised foam is then pulled off by hand using unspecified force in an unspecified manner. In the event that the coating fails to be revealed, the foam may be scraped with an unspecified knife under unspecified conditions, using unspecified force. If the coating again fails to be revealed, the coating is acceptable. A second foam/metal specimen is subjected to 100% humidity at elevated temperature for 24 hours, and the foam pulled off by hand, again under no standardised conditions.

If the coating is revealed in either test, the specimen 'fails'.

It is difficult to see what objective is served by either of these European standards. At least, the latter does no harm.

References

1. BS EN 13523-16: 2004 Coil Coated Metals - Test Methods. Part 16. Resistance to abrasion [Return ]

2. BS 3900: Part E15: 1997 and ISO 7784-2: 1997 (identical texts) Methods of test for paints. Determination of resistance to abrasion (Rotating abrasive rubber wheel) [Return ]

3. CEN/CENELEC Internal Regulations Part 3: 1999 page 24 [Return ]

4. BS EN 13523-20: 2004 Coil Coated Metals - Test Methods. Part 20. Foam adhesion [Return ]

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